In recent years, an analog transmission scheme and a digital transmission scheme have been known as a transmission scheme in a radio transmission system (for example, see Patent Document 1).
The analog transmission scheme can be automatically adapted to the state of a radio channel (radio propagation path), and thus, information amount according to a channel state can be transmitted. In other words, in the analog transmission scheme, the transmission performance automatically improves as the state of the radio channel improves. However, in the analog transmission scheme, it is difficult to secure transmission of information.
On the other hand, in the digital transmission scheme, an optimal amount of information can be transmitted and secure transmission can be performed, by switching between transmission methods (a modulation scheme and an error correction coding scheme). However, in the digital transmission scheme, if a transmission method not suitable for the channel state is used, there is a problem that the channel capacity cannot be fully utilized or information cannot be transmitted at all. Further, in the digital transmission scheme, there is a problem that a processing load and an overhead are increased by having complex control such as measuring the channel state and feeding the measurement result back.